Heating apparatus with a heat exchanger

ABSTRACT

A heating apparatus including a burner and a heat exchanger wherein the burner supplies a primary fluid and exhaust gas to the heat exchanger. Secondary fluid supplied to the heat exchanger is first heated within the heat exchanger by the primary fluid and then is further heated within the heat exchanger by the exhaust gas.

The present invention relates to heating apparatus, preferably such asare oil-fired, which include a heat exhanger, and which are intended forsupplementing or replacing conventional heating installations, e.g. forsmall house boilers and the like.

As a result of increases in the price of oil, and since oil isoccasionally a commodity difficult to obtain, it has become more andmore desirable to obtain effective installations for heating purposeswhich are economical with regard to fuel and which also have a lowprice. This invention is described, per se, in connection with problemsconcerning one-family houses, but one skilled in the art will understandthat the invention has many conceivable applications and is thus notrestricted to this field.

There are oil-fired heat exchangers provided with equipment such thatthe flue gases can give their heat content to the fluid which is to beheated and which conveys the heat to such as radiators in a building. Incertain cases, there is thus a pre-heater placed in the flue gas passagefor also pre-heating the fluid which distributes the heat. However, thisis not a particularly good solution if it is taken into considerationthat the flue gases contain substances, which can condense and formcoke-like deposits as well as forming corrosive substances which can putgreat requirements on the material in the heat exchanger and flue gaspassage. In addition, such installations will be voluminous.

A desire is therefore to achieve a combustion-driven heat exchanger, inwhich the heat in the flue gases is recovered to a certain extent andused for heating purposes. Another desire is to achieve a compact andcheap unit, which can easily be connected into the system as required.

The present invention has the object of providing a combustion-drivenheat exchanger while mitigating the above-mentioned problems, and whichsatisfies the mentioned desires. This object is achieved by a structureof the kind disclosed in the claims, which also disclose what ischaracteristic for the invention.

The invention will now be described in more detail in the following inconnection with the accompanying drawings, where

FIG. 1 is a schematic cross section through a heat exchanger included ina heating apparatus in accordance with the invention, and

FIG. 2 is a longitudinal section through the heat exchanger of FIG. 1.

The heat exchanger 1, schematically illustrated in the Figures, isgenerally tubular in shape, and comprises an exterior shell 2,surrounded by an insulating casing 3, inside of which there is athrough-going tube 4, which defines a circular chamber 5 for the primaryfluid, i.e. the heating fluid, where the shell 2 constitutes the outerwall and the tube 4 the inner wall, walls 6 and 7 closing off thechamber 5 axially, while the interior of the tube 4 forms a passage 8for exhaust gases from a burner. The passage 8 is provided with an inlet9 and an outlet 10, both of which have a lesser diameter than the tube 4for giving the exhaust gases a decreasing volocity in the throughpassage 8 compared with that in the inlet 9 and outlet 10.

A pipe 11 for conducting secondary fluid, i.e. the fluid which is to beheated, extends helically through the chamber 5 round the tube 4 andthrough the tube 4 to the passage 8 for flue gases, where the pipe 11 isextended in several loops going backwards and forwards in thelongitudinal direction of the passage 8. An expansion tank 12 isconnected to the chamber 5 and is provided with a safety valve 13 forpreventing an explosion in the heat exchanger in the case ofoverheating, the tank also being provided with a venting valve 14.

All fluid connections are placed in the same end wall 7. The connection15 for incoming primary fluid is arranged at the bottom of the chamber 5and extends almost up to the opposite end wall 6, where the fluid heatedby the burner flows into the chamber 5, and is kept in circulation withthe aid of a pump associated with the burner and similarlyunillustrated. At the upper part of the chamber, there is an outletconnection 16 for the primary fluid and this extends only as far as ashort distance through the end wall 7.

An inlet connection 17 for secondary fluid is placed above the tube 4and extends towards the opposite end wall 6 where it is helically formedround the tube 4 such as to extend back towards the end wall 7 throughwhich the inlet it passes, and at this end wall the pipe 11 is takenthrough the tube 4, where it forms the previously mentioned loops foronce again being taken through the tube 4 adjacent the end wall 7 topass out through this wall in the form of the outlet 18.

The tube 4 has an inlet 9 at the end wall 6 and an outlet 10 at the endwall 7. Since the inlet 9 and outlet 10 have considerably less diameterthan the tube 4, there are tapering transitions 19, 20 at the junctionsbetween the tube 4 and the inlet 9 and outlet 10. All leads-through andconnections are both liquid and gas tight.

An oil burner with at least two power steps is preferably utilized. Thisburner heats up the primary fluid, which suitably consists of a liquid,e.g. water, which is pumped from the region heated by the burner via theinlet 15 into the chamber 5 where it gives off its heat to the secondaryfluid through heat exchange, and returns from the outlet 16 for furtherheating.

The secondary fluid, e.g. a liquid in a heating system, is pumpedthrough the inlet 17 and through the pipe 11, first through the helixwhich is placed in the chamber 5, where the secondary fluid is given afirst heating, and thereafter through the loops in the passage 8 whereit is given further heating before it leaves the heat exchanger.

From the burner, the flue gases, which have a temperature of over 200°C., suitably at least 240° C., flow in through the inlet 9 and into thepassage 8, where the flue gases pass over the loops of the pipe 11 inthis passage 8 as well as against the inner wall of the tube 4. Heat isthus transferred from the flue gases to both the primary fluid andsecondary fluid. The diameter of the passage 8 is adjusted in relationto the diameters of the inlet 9 and outlet 10 such that the flue gasesobtain a given residence time in this passage 8 and the exhaust gasesflowing out through the outlet 10 thus have a temperature which does notfall below 100° C. This means that he temperature on the inside of thetube 4 as well as the outside of the loops of the pipe 11 in the passage8 have a temperature of over 100° C. There is thus achieved that thecondensation point of the flue gases is below the temperatures which thedifferent parts have, and there are thus no deposits of coke-likesubstances and corrosive substances on the parts in question. In turn,this results in that cleaning is avoided and that the parts have a longlife.

A contributing reason for the heat exchanger actually functioning isthat the flue gases are not used for pre-heating of the secondary fluid,but for post-heating of it after it has been given a first supply ofheat through the primary fluid. There is thus achieved that thetemperature differences between the combustion gas and the secondaryfluid are moderate, and above all sufficiently high for the flue gasesto keep the surface temperature of the tube 4 and the loops in thepassage 8 about 110° C.

Conventional control equipment is, of course, included in the heatingapparatus with a heat exchange in accordance with the invention, formaintaining constant, pre-determined temperatures and differentoperational controls of the burner and pumps.

The object of mentioned in the introduction has been achieved by thepresent invention, and a heating apparatus with a heat exchanger hasbeen obtained which is effective, compact and cheap and which requiresminor service. One skilled in the art will, however, understand that theinvention can be modified in many ways, but such modifications areintended to lie within the scope of the accompanying claims.

We claim:
 1. Heating apparatus including a burner connected to a heatexchanger (1), the burner heating a primary fluid which circulatesthrough the heat exchanger (1) to transmit heat of the primary fluid toa secondary fluid in the heat exchanger (1), the heat exchanger (1)being provided with a tube (4) which extends through the heat exchangerand through which exhaust gases from the burner flow, the heat exchanger(1) including a chamber (5) which surrounds the tube (4) and throughwhich the primary fluid flows, as well as a pipe coil (11) through whichthe secondary fluid flows, the pipe coil (11) being disposed into thechamber (5), around the tube (4), and then through a wall of the tube(4) into a passage (8) within the tube (4), the pipe coil forming one ormore loops in the passage (8) and then extending out of the heatexchanger (1), the pipe coil (11) being so disposed so as to lead thesecondary fluid first through the primary fluid in the chamber (5) andthereafter through the exhaust gases as the exhaust gases flow throughthe tube (4), the exhaust gases being led through the passage (8) forheating the wall of the tube (4) as well as said one or more loops. 2.Heating apparatus in accordance with claim 1, wherein the heat exchanger(1) is made as a substantially cylindrical container, through which thetube (4) for the exhaust gases is axially extended.
 3. Heating apparatusin accordance with claim wherein the diameter of the passage (8) isgreater than an inlet (9) for the exhaust gases entering the passage(8).
 4. Heating apparatus in accordance with claim 2 wherein thediameter of the passage (8) is greater than an inlet (9) for the exhaustgases entering the passage (8).
 5. A heating apparatus, comprising:aheat exchanger including:an inner fluid chamber having an inlet and anoutlet and disposed within a first tubular wall; and an outer fluidchamber having an inlet and an outlet and disposed between said firsttubular wall and a second tubular wall which is concentric with saidfirst tubular wall; a burner attached to said inlet of said inner fluidchamber and to said inlet of siad outer fluid chamber for supplying anexhaust gas to said inner fluid chamber and a primary fluid to saidouter fluid chamber, respectively; and a conduit for supplying asecondary fluid to said heat exchanger, said conduit having an inlet, anoutlet and a length extending therebetween, said inlet and said outletbeing attached to said heat exchanger and said length being disposedwithin said heat exchanger, said length extending from said inlet ofsaid conduit into said outer fluid chamber, then through said firsttubular wall into said inner fluid chamber, and then from said innerfluid chamber to said outlet of said conduit.
 6. The heating apparatusof claim 5 wherein said length includes a first length which extendsfrom said inlet of said conduit, then is coiled around said firsttubular wall and then extends through said first tubular wall into saidinner fluid chamber, and a second length which forms one or more loopswithin said inner fluid chamber, then extends back through said firsttubular wall into said outer fluid chamber and then extends to saidoutlet of said conduit.
 7. Heating apparatus in accordance with claim 6,wherein the heat exchanger is made as a substantially cylindricalcontainer, through which the tube for the exhaust gases is axiallyextended.
 8. Heating apparatus in accordance with claim 7 wherein thediameter of the inner fluid chamber is greater than an inlet for theexhaust gases entering the inner fluid chamber.